Endoscopes are used for a variety of medical diagnostic and therapeutic indications. There are numerous endoscopes specifically designed for the examination of body parts including the esophagus, stomach and duodenum, colon, blood vessels, bronchi, the peritoneal cavity, joint spaces, etc. Such medical devices/probes have the ability to provide images from inside the patient's body. Considering the potential damage to a human body caused by the insertion of a foreign object, it is preferable for the probe to be as small as possible for many applications. Additionally, the ability to image within small pathways such as small vessels, small ducts, small needles, cracks etc., requires a small probe size.
When the endoscope needs to be small, either to reach small or difficult to reach parts of the body or to reduce trauma, the difficulty and ability to make and use endoscopes becomes much more challenging. For example, it is difficult to form an effective imaging window while maintaining ultra-thin window and side-wall thicknesses. Similarly, the endoscope and method of making the same and fitting in the various components with the necessary clearances into a small outer profile is technically challenging. Thus, there is a need for new miniature and micro-miniature endoscopes with enhanced performance and methods of making such endoscopes in a cost effective manner.
There have been numerous known approaches to reducing the size of endoscopes (i.e., achieving further miniaturization) for various specific imaging techniques such as optical coherence tomography (hereinafter referred to as “OCT”) and spectrally encoded endoscopy (“SEE”) or the like over the years.
In order to obtain an optical image of a surface using OCT or SEE, the surface of the subject study area has to be scanned with an optical beam. Currently, the most common method for scanning is to “rotate” a signal transmitting optical fiber with some turning/focusing optics located on its distal end.
An example of the “rotating” approach is disclosed in International PCT Publication WO 2016/077252 to Leo D. Didomenico, entitled “Wide-angle, broadband, polarization independent beam steering and concentration of wave energy utilizing electronically controlled soft matter”, published May 19, 2016, (hereinafter referred to as “DIDOMENICO”) which provides a general method for electronically reconfiguring the internal structure of a solid to allow precision control of the propagation of wave energy. The method allows digital or analog control of wave energy, such as but not limited to visible light, while maintaining low losses, a multi-octave bandwidth, polarization independence, large area and large dynamic range in power handling. Embodiments of such technique are provided for large-angle beam steering, lenses and other devices to control wave energy.
A downside to the “rotating” approach, however, is that it requires quite elaborate mechanics to rotate the fiber and a complicated optical alignment on the proximal end of the fiber, while suffering from image irregularities caused by non-uniform rotational distortions (NURD). Moreover, other devices utilize optical rotary junctions which suffer from the same technical drawbacks.
Another method of scanning using an optical beam is to obtain an optical image of a surface using OCT or SEE using “micro-miniature motors” is to rotate a scanning optical component (e.g. mirror) in front of the distal end of a stationary optical fiber.
An example of the “micro-miniature motor” approach is disclosed in publication entitled “Development of a high-speed synchronous micro motor and its application in intravascular imaging” to Wang et al., Sensor and Actuators A 218 (2014) 60-68, (hereinafter referred to as “WANG et al”.) which discloses the design, fabrication and characterization of a synchronous micro motor which consists of flex print coils and a permanent magnet rotor. The size of the motor is 2.0 mm length and 1.0 mm outer diameter. With 1.0 A effective driving current, the motor can rotate a 0.3 mm mirror at a maximum speed of 3640 revolutions per second. An application of the micro motor may be used as a distal actuator for intravascular imaging.
A second example of the “micro-miniature motors” approach to rotate a scanning optical component (e.g. mirror) in front of the distal end of a stationary optical fiber is disclosed in U.S. Pat. No. 9,513,276 to Tearney et al., entitled “Method and Apparatus for Optical Imaging via Spectral Encoding”, published on Feb. 19, 2015, (hereinafter referred to as “TEARNEY et al.”) which describes a method and apparatus for endoscopic confocal microscopy which circumvents the need for miniature, high-speed scanning mechanisms with a probe. Spectrally encoded confocal microscopy (“SECM”) is a wavelength-division multiplexed confocal approach that may be used which utilizes a broad bandwidth light source and can encode one dimension of spatial information in the optical spectrum.
While the aforementioned approaches disclosed in both WANGA et al. and TEARNEY et al. simplifies the design of the endoscopic instrument, motors of such a small size are quite difficult and expensive to manufacture. In addition, electric motors tend to generate heat while rotating and needs measures to dissipate heat produced by this motor.
In lieu of the “rotating” optical fiber approach requiring elaborate mechanics (such as rotating optical-junctures) to rotate the fiber and having a complicated optical alignment on the proximal end of the fiber, while suffering from irregularities caused by NURD (see above DIDOMENICO); and in lieu of the “micro-miniature motor” on a distal end of an instrument approach (see above WANGA et al. and TEARNEY et al), scientists, researchers and inventors have looked towards electrowetting-based optical devices to provide an advantageous, versatile, and cost effective alternatives to the previous methods discussed above.
Electrowetting devices, and in particular electrowetting lenses and prisms, are known in the art, and generally comprise a refractory interface between first and second immiscible liquids that is moveable by electrowetting. Such devices have a number of attractive features including transmissive geometry, small size, low operating voltages, fast response time, low insertion losses, polarization insensitivity, large stroke and good optical quality. These favorable properties make utilizing electrowetting lenses a more versatile solution than technologies such as spatial light modulators, micro-electro-mechanical segmented (MEMS) and deformable mirror systems, piezo-actuated deformable mirrors, and flexible membrane liquid lenses. (excerpt from WO 2015/112770 to Gopinath et al below).
An example of utilizing electrowetting optics technology in endoscopes is disclosed in International PCT Publication WO 2015/112770 A1 to Gopinath et al., entitled “Optical imaging devices and variable-focus elements, and methods for using them”, published Jul. 20, 2015, (hereinafter referred to as GOPINATH et al.) which relates to optical imaging devices and methods useful in biological and medical imaging applications. In one embodiment, an optical imaging device includes a flexible lightguide. An output of a source of pulsed infrared radiation is optically coupled to a first end of the flexible light guide. A lens assembly is attached to and optically coupled to a second end of the flexible lightguide. A lens assembly includes a variable-focus lens element having a tunable focal length and a photodetector coupled to the flexible lightguide to detect radiation propagating from the second end toward the first end of the flexible light guide. Such above described optical imaging devices and methods can be used in both confocal and multi-photon techniques.
And still yet another example of utilizing electrowetting optics technology in endoscopes is disclosed in publication entitled “Miniature, minimally invasive, tunable endoscope for investigation of the middle ear” to Pawlowski et al, Biomed Opt Express 2015 Jun. 1; 6(6): 2246-2257 (hereinafter referred to as “PAWLOWSKI et al.”) which discloses a miniature, tunable endoscopic probe for facilitating examination of the auditory system. The distal end of the rigid endoscope is designed to allow for safe insertion into the tympanic chamber through a small incision in the tympanic membrane (myringotomy). To achieve this goal, the distal end of the rigid endoscope is encapsulated into a hypodermic tube with an outer diameter of 1.4 mm. Tunability, provided by incorporation of the electrowetting lens, allows the operator to electronically move the object plane along the optical axis, providing imaging capability beyond the depth of field of a static optical system. Since movement of the plane of the best focus is facilitated by an electronically controlled change of curvature at the interface between two immiscible liquids within the tunable lens, the distal end of optical system can be held stationary at a safe distance away from the auditory apparatus. The miniature tunable endoscope is further capable of sharp imaging of anatomical features of parts of the ossicular chain, providing objective and quantitative morphological data.
However, while it is noted that while U.S. Patent Publication No. 2007/0156021, PCT Publication WO 2015/112770 A1 and PAWLOWSKI et al. address adaptive electrowetting features utilized for focusing, tuning focal length and zooming function in endoscopes, there has yet to be developed and/or proposed miniature endoscopes which utilize electrowetting features for obtaining an optical image of a surface using OCT or SEE techniques to scan the surface of a subject study area with an optical beam which (1) has a simplified design that does not use rotating mechanical components (as an alternative to optical rotary junction and micro-miniature motors), (2) has low non-uniform rotational distortions (NURD), and (3) allows for dimensional scaling down to molecular level.
Accordingly, with regard to investigation of internal organs with ultrahigh resolution, OCT and SEE miniaturized endoscopic probes that can be positioned in the vicinity of the respective biological surfaces are needed so that minimally invasive cross-sectional images in vivo, can be effectively used to assess the health of patients in a safe, effective, economical and painless manner which meet the such requirements.
Hence, it would be advantageous to have a scanning element at a distal end of an imaging fiber of a medical instrument, such as a miniature endoscope or a micro-miniature endoscope, that does not have any moving parts and is small enough to be compatible with the size of the optical fiber which (1) has a simplified design that does not use rotating mechanical components (as an alternative to optical rotary junction and micro-miniature motors), (2) has low non-uniform rotational distortions (NURD), and (3) allows for dimensional scaling down to molecular level.
In view of the these considerations, there is a need to address and/or overcome at least some of the deficiencies described herein above.